The present invention relates to compositions comprising an epoxy resin and, as curing agent for the epoxy resin, a polyol and, as accelerator, a microgel-amine salt or microgel-imidazole salt, and also to crosslinked products obtainable by curing such compositions.
Nitrogen-containing bases are well known to the person skilled in the art as curing agents or curing accelerators for epoxy resins. Such systems have, however, only limited storage stability because those bases react with epoxides even at relatively low temperature, in some cases even at room temperature, which is manifested in an increase in the viscosity of the epoxy resin formulation and, on prolonged storage, results in gelation of the mixture. The greater the reactivity of the nitrogen-containing base, the lower the storage stability of the epoxy resin mixture and the shorter the pot life. For that reason, such systems are formulated as two-component systems, that is to say the epoxy resin and the nitrogen-containing base are stored separately and mixed only shortly before processing.
There has been no shortage of attempts at improving the storage stability of such systems by developing appropriate curing systems. The problem posed is the more complex because, at the same time as the requirement for a high storage stability and a long pot life, there should not be any deterioration either in the reactivity at the desired curing temperature or in the properties of the fully cured materials.
EP-A-304 503 describes masterbatches of encapsulated materials and epoxides as latent curing agents for epoxy resins, wherein the core material is a tertiary amine in powder form, which is surrounded by a shell of the reaction product of the same amine with an epoxy resin.
A similar curing system, but with a core material of an amine and an anhydride, is disclosed in JP-A-Hei 02-191624.
Although such latent curing agents and accelerators based on encapsulated particles are suitable for producing storage-stable one-component systems, they have the disadvantage of inadequate stability with respect to mechanical influences, such as shear forces and compressive loads.
BCl3 complexes also have good latency, but fumes are formed at temperatures above 160xc2x0 C., prohibiting their use in epoxy-resin-based casting resins because the mould temperatures are at or above that temperature.
EP-A 0 816 393 describes latent epoxide curing systems (based on anhydride curing agents in combination with salts of COOH-group-containing microgels and nitrogen bases) having an improved pot life, which have high stability with respect to mechanical stress in the form of shear forces and, in addition, result in cured mouldings that have a high glass transition temperature and a high thermal stability. The latency of those systems is, however, capable of further improvement, especially at elevated temperatures.
EP-A 0 633 286 describes curable epoxide curing systems for the production of moulded articles having high-gloss surfaces, comprising an epoxy resin, a curing agent and, as fillers, wollastonite and a quartz/kaolinite mixture. The latency of such systems is, however, like-wise capable of further improvement.
The aim of the present invention was to make available epoxide curing systems having good storage stability, good reactivity under curing conditions, good and at the same time highly varied processing possibilities, even at elevated temperatures, and, finally, good properties of the fully cured materials.
It has now been found that compositions comprising an epoxy resin and, as curing agent for the epoxy resin, a polyol and, as accelerator, a solid microgel-amine salt or a solid microgel-imidazole salt have the desired property profile.
The present invention accordingly relates to a composition comprising
(a) an epoxy resin having, on average, more than one 1,2-epoxy group per molecule,
(b) a polyol as epoxy resin curing agent and
(c) a solid reaction product of a carboxylic-acid-group-containing microgel and a nitrogen-containing base (microgel-amine adduct) as accelerator.